The use and abuse of alcohol among American Indians (AI) is a major public health concern. To date, the best information derives from adolescent populations. Compared to their non-AI counterparts, AI youth are more likely to use alcohol, more likely to become problem drinkers, more likely to meet diagnostic criteria for alcohol abuse and dependence, more likely to use alcohol in combination with drugs, and more likely to have both an alcohol use disorder and a psychiatric disorder. From service system data and vital statistics, we know that AIs generally are more likely to develop a variety of physical health conditions that are related to alcohol use and to die from alcohol-related causes. Research to date also suggests that rates of the alcohol-related health disparities (ARHDs) vary substantially across AI tribes. Despite the compelling nature of these disparities, surprisingly little is known regarding key aspects of their descriptive and analytical epidemiology. Indeed, the specific relationships of alcohol use, abuse, and dependence with co morbid drug, psychiatric, and physical health conditions among AI adults are largely unexplored. Yet findings from studies focused on the US general population suggest that these interrelationships are critical for understanding ARHDs. The goal of this project is to analyze data from the recently completed American Indian Service Utilization, Psychiatric Epidemiology, and Risk/Protective Factors Project - the first large-scale, population-based study of AIs between the ages of 15 and 54. The specific aims for this project are as follows: 1) to describe disparities in the epidemiology of alcohol use across 2 AI population-based samples of 15-54 year-olds as well as between these 2 AI samples and samples representative of the US general population; 2) to conduct a parallel investigation regarding disparities in the epidemiology of alcohol abuse and dependence in these same samples; 3) to extend this line of inquiry to explore disparities in the epidemiology of drug use, abuse, and dependence co morbid with alcohol use, abuse and dependence; 4) to depict disparities in the epidemiology of non-substance use psychiatric disorders co morbid with alcohol use, abuse, and dependence; and 5) to investigate disparities in the epidemiology of physical health conditions co morbid with alcohol use, abuse, and dependence across these 2 AI tribes and between these tribes and the US general population.